Florida Roofing Underlayment Requirements
Florida’s roofing underlayment requirements are evolving to better protect homes against storms, moisture, and rising insurance risks. Roofing underlayment is a protective layer placed between the roof deck and the roofing material. It acts as a secondary water barrier, providing extra protection against rain, wind-driven moisture, and leaks in case the outer roofing material is damaged or fails.
Understanding the updated rules and your options is critical for protecting your investment and staying compliant with Florida’s building codes. Compliance is important whether you’re replacing your roof or building a new one. It helps you protect your investment and avoid costly problems.
Building Code Underlayment Updates for 2025
Florida’s building code updates introduce stricter rules for underlayment placed during roof installation to address increased storm activity and water intrusion.
All roofing systems in Florida must include underlayment that meets or exceeds ASTM (American Society for Testing and Materials) standards for water and wind resistance. This applies to both new constructions and re-roofing projects.
The 2023 Florida Building Code (FBC) is continuously reviewed, corrected, and updated to reflect evolving building practices and environmental challenges.
Key updates include the following:
Approved Materials for Roof Underlayment
Roof underlayment must comply with one of the following ASTM standards:
- ASTM D8257
- ASTM D226 Type II
- ASTM D4869 Type III or IV
Dual-Layer Underlayment Installation
To ensure effective waterproofing and wind resistance, the Florida Building Code now requires a dual-layer underlayment installation for metal, metal shingle, slate, slate shingle, asphalt shingle, and mineral surfaced roll roofing.
Dual-layer underlayment installation begins with a starter strip of underlayment, which is half the width of a full sheet, placed along the eaves and properly secured. A full-width reinforced underlayment sheet is then applied as the second layer, starting at the eave.
Each new layer should overlap the sheet below by half its width plus 2 inches for the first overlap. All following layers should overlap by half the sheet’s width plus 1 inch to ensure proper coverage and protection.
Dual-layer underlayment installations offer superior water resistance, improved wind resistance, and added durability. They provide enhanced protection and performance in heavy rains, hurricanes, and high humidity compared to traditional single-layer installations.
Key Technical Updates and Code Revisions
Several important adjustments have been made to improve installation consistency.
The Florida Building Code (section 1518.12) was updated. The width of self-adhering modified bitumen membranes changed from 3 ¾ inches to 95 mm. The changes comply with ASTM D1970 (flexible flashing tape) standards.
These changes help clarify the requirements for properly installing dual-layer underlayment systems.
Important Changes to Nail and Material Standards
Two significant updates have been made to the material and nail standards.
The ASTM D6757 now replaces the older ASTM D675 specification. Additionally, the minimum nail penetration depth through wood sheathing has been reduced from 3/16 inch to 1/8 inch for better fastening consistency and reliability.
These updates help ensure a more secure and durable roofing system, especially under Florida’s demanding weather conditions.
New Guidelines for Tile Roof Underlayment
Specific requirements now govern underlayment installation for tile roofing.
These apply to mechanically fastened tile systems using counter battens or direct-deck installation methods. Roofs with a pitch of 4:12 or greater, or those with single-ply underlayment on battens or direct deck, are no longer classified as nail-on underlayment systems.
Improper installation may result in code violations, insurance issues, and even voided warranties. To ensure compliance and long-term protection, always work with a licensed contractor who stays up-to-date with code changes.
Secondary Water Barriers
Secondary water barriers provide extra protection if the main roof covering is blown off during a storm. This additional waterproof layer is installed beneath the primary roof to prevent water intrusion in severe weather, especially in hurricane-prone areas.
In certain parts of Florida with higher hurricane risk, secondary water barriers are commonly required or recommended.
How Secondary Water Barriers Are Installed
A secondary water barrier is installed to seal roof deck joints and protect against storm damage.
Roofing professionals will complete the following steps to install a secondary water barrier:
- Prepare the roof deck and ensure it’s dry and clean.
- Apply the self-adhering tape to seal the deck and panel joints.
- Install underlayment over the entire deck.
- Seal flashings and penetrations.
- Install the desired roofing material (shingles, tiles, metal panels, etc.).
This practice is most often seen in coastal regions, re-roofing projects, and roofing upgrades. The goal is to help reduce water intrusion and potential damage during storms, particularly in regions that experience frequent high winds and heavy rain.
Why These Requirements Matter in Florida’s Climate
Underlayment is a home’s defense against wind-driven rain and water intrusion. Florida’s combination of hurricanes, heavy rains, and humid conditions makes roofing underlayment an important layer of protection.
With the rising cost of homeowners insurance and frequent extreme weather events, following these 2025 standards gives you peace of mind. It may even reduce your insurance premiums.
The latest Florida Building Code updates have introduced stricter inspection requirements and new material standards, focusing on durability and resilience against high winds and heavy rain. These changes align with the updated ASCE 7-22 wind load standards, which redefine wind design requirements for Florida’s storm-prone regions.
By choosing approved underlayment and making sure it’s installed correctly, you’re meeting an important legal requirement. You’re also investing in the long-term safety and value of your home.
Common Underlayment Mistakes to Avoid
Many homeowners unknowingly compromise their roofs by selecting the wrong underlayment or skipping code requirements.
Avoid these pitfalls:
- Using outdated materials that no longer meet 2025 standards
- Skipping the secondary water barrier in coastal zones
- Hiring unlicensed contractors who are unfamiliar with the newest FBC changes
- Failing to confirm local code variations, especially in HVHZ-designated counties
- Overlooking proper installation techniques for dual-layer systems
- Ignoring underlayment overlap and fastening requirements
- Not verifying that materials meet approved ASTM standards
- Choosing cost over quality without understanding long-term durability risks
Ask your contractor to walk you through the underlayment specs in your proposal if you’re unsure.
Following the 2025 Code Matters for Every Homeowner
Make sure you follow Florida’s roofing laws to protect your home, keeps yourself compliant, and ensure your roof performs efficiently in extreme weather conditions.
Florida homeowners face unique challenges, from hurricanes to high humidity. The updated building code aims to address these risks by reinforcing roof systems from the inside out. Choosing the right underlayment and ensuring it’s installed to code will help you safeguard your home and your investment for years to come.
